1. Field of the Invention
The present invention relates to a transmission and a vehicle provided with the transmission.
2. Description of the Related Art
Transmissions which are used for motorized vehicles, such as a motorcycle, include a type using a rotary shift drum, where some transmissions of this type include a mechanism called a rotary stopper. This mechanism is provided to restrict shifting from top gear into a neutral position during running of the vehicle in a transmission in which gears are shifted from top gear (for example, 4th gear) into the neutral position directly as being shifted from the neutral position into 1st gear, 2nd gear, and further into higher gears so as to increase a gear ratio because a sudden engine brake is generated, for example, when the gears are shifted from 4th gear into the neutral position and further into 1st gear during running of the vehicle.
As such a mechanism, for example, JP 57-138484 A discloses a gearbox for a motorcycle provided with a rotary stopper having the following structure. A friction spring is fitted and frictionally engaged in a recessed groove provided in a side surface of a high-speed driven gear. The friction spring biases a locking piece so as to swing the same during rotation of the high-speed driven gear. The locking piece engages with an engagement portion of a shift drum to thereby prevent the shift drum from rotating to a low-speed shift position.
Further, JP 64-049743 A discloses a gearbox for a vehicle provided with a rotary stopper having the following structure. A rocker arm is biased by a friction spring frictionally engaged on a boss portion 62 of a second gear 29B, and is pivotally fitted to a shift fork shaft.
JP 57-012163 A discloses a gearbox for a motorcycle provided with a rotary stopper having the following structure. A friction spring is frictionally engaged on a center boss spline-coupled to an output shaft, and the friction spring biases a locking piece.
As a member with which the friction spring is frictionally engaged, the above-mentioned mechanisms require a gear that additionally has a special structure such as the recessed groove or the boss portion, or require a member that costs time and money for processing the center boss or the like to include a spline groove. This leads to an increase in the cost of the rotary stopper mechanism.
Further, the friction spring is frictionally engaged with a member coupled to the output shaft of the transmission, and hence a sliding portion of the friction spring generates heat by friction during rotation of the output shaft. Lubricating oil can be sufficiently supplied to the sliding portion of the friction spring during operation of the engine, and hence the sliding portion is lubricated and cooled. However, in a case where the engine is stopped, for example, and if the vehicle is in a neutral state and running down a slope at high speed, the sliding portion of the friction spring may be heated to a high temperature.